The Seafaring power still exists in decline, otherwise you'd have to remove tokens from the sea/lake when going into decline with any race. Since ghouls can continue to conquer as normal when in decline, it seems OK that they can still conquer new seas or ones they abandoned.

Tactically abandoning then reconquering is a bad play, and probably a bug.

I noticed this bug just today. I thought it was just a neat rule that I'd overlooked, but then I look at the SW rules sheet that says "As long as your seafaring race is active, you may conquer the Seas and the Lake".

Though I'll grant there is some wiggle room in that the Ghouls description claims that they conquer "playing exactly as if they were still Active tokens".

The official clarification thread lists ID Ghouls as not being able to conquer new ones, btw. Though there was a ton of going back and forth on it, I never saw any OFFICIAL DOW comment on it. I don't want to rehash all those reasons because I see the argument on either side, though personally the difference in what's on the badge on one side versus the other clinches it for me.

Would be nice to find out an official ruling, especially in light of how they work in the app.

The Official answer is that In Decline races cannot conquer water regions. The app is doing this situation wrong, I'm afraid.

Sorry to disappoint.

EDIT: I looked back at the FAQ thread and in the first post this rule is clearly stated. Ghouls may not continue to attack water regions. That thread is the Official FAQ thread for the base game, so even though it isn't written by DoW staff it is official because they would have corrected it if the rule was wrong.

Thanks for double checking that Ras. I was pretty sure of the current stance on it. It's just the official answer was also that catapult could be used multiple times a turn as long as you didn't move it. That turned out to be wrong and the app had it right. While it's highly unlikely to work out the way I hope it will, I would love to see the app be the correct play here again.